Production of alkali metal fluoborate



United States Patent Offlce Patented Jan. 28, 1964 3,119,654 PRODUCTIONOF ALKALI METAL FLUOBORATE George L. Cunningham, Allentown, Pa.,assignor to W. R. Grace & Co., New York, N.Y., a corporation ofConnecticut No Drawing. Filed May 2, 1961, Ser. No. 107,037 Claims. (Cl.23-59) This invention relates to a process for the production offluorine values. In one specific aspect, this invention deals with aprocess for the production of alkali metal fluoborate.

One process previously known for making the alkali metal fluoborates hasinvolved treating fluoboric acid with an alkali metal hydroxide,carbonate, or other salt. Fluoboric acid as most commonly made by themethod using hydrofluoric acid and boric acid or boric oxide has beenrelatively expensive. Consequently, the current process for makingalkali metal fluoborate is also necessarily expensive. Fluoboric acidhas also been made by reacting acid grade fluospar 'with sulfuric acidand boric acid or boric oxide, but this process offers littleimprovement in cost. The necessity of using relatively pure fluoboricacid as one of the reactants in the production of alkali metalfiuoborates increases the expense of the process in accordance with thecost of the acid.

As is well known, when phosphate rock, which commonly contains 2.5 to4.5% of fluorine, is acidified with a strong mineral acid, gasescontaining fluorine are evolved. In the customary process of makingsuperphosphate fertilizer, fluorine-containing gases are evolved fromthe mixer in which the acid and rock, in finely divided form, are mixedand from the so-called den in which the mixture is stored. These gasesgenerally are free or substantially free of phosphate. When phosphoricacid is concentrated by evaporation, the gases evolved from the acidconcentrator also generally contain fluorine compounds. Thesefluorine-containing gases, in which the fluorine is present principallyas silicon tetrafluoride are scrubbed with water. This is an old,well-known and highly eflicient method for the recovery of fluorine fromsuch gases, and solutions containing from 2% to 30% or more of H SiF areobtained. This, then is used to prepare numerous by-products, among themore commonly made ones of which are alkali metal fluorides, ammoniumfluoride, and ammonium acid fluoride.

It is an object of this invention to provide an economical process forthe production of alkali metal fiuoborates.

It is a further object of this invention to avoid the use of bothhydrofluoric acid and boron tetrafluoride in alkali metal fluoborateproduction.

It is still a further object of this invention to provide a new andimproved process for the preparation of alkali metal fluoborates insubstantial yields from readily available ammonium fluoride, alkalimetal fluoride and boric acid or boric oxide.

The process of the present invention is based on the discovery that analkali metal fluoride will react with ammonium fluoride or ammonium acidfluoride, and boric acid or boric oxide in aqueous solution to form thealkali metal fluoborate. The process has other advantages beyond itsbasically economic character in that it is not dlfficlllt to carry out.In the process of the invention the reactants can be brought together asaqueous solutions, they may be added as solids to a limited amount ofwater such that a slurry is produced, or they may be reacted together assolids. In any case, when the temperature is raised ammonia and waterare evolved, and the process is continued until the mass is solid. Thesolid remaining will be practically pure alkali metal fluoborate.Instead of using the normal alkali metal fluoride, the alkali metal acidfluoride, such as sodium acid fluoride or potassium acid fluoride may beused. The amount of water is not critical, but it should be understoodthat to cause the reaction to go to completion, the ammonia and watermust be evaporated off and thus the use of excess water will increasethe cost of evaporation.

The fluoride salts used as reactants in the process of the invention maybe the normal fluoride or the acid fluoride or a mixture of the twosalts. The amounts added are not critical but, in order to obtainsubstantially pure alkali metal fluoborates, they should be instoichiometric ratio. If excess alkali metal fluoride or acid fluorideis used, the resulting product will contain alkali fluoride or alkalimetal acid fluoride. If excess ammonium fluoride or ammonium acidfluoride are used, the product will be a complex containing in excess offour atoms of fluorine per molecule of salt. The impure alkali metalfluoborate obtained in the first step may be purified by crystallizationfrom water.

The general reactions of the aforementioned process can be representedas follows, using sodium as an illustrative example:

The following examples are given for purposes of illustration and arenot intended to limit the scope of the invention in any way.

Example I 14.0 parts of NaF, 37.04 parts of NH F and 11.61 parts of 13 0were placed in parts of water. The solution was evaporated to dryness.17.0 parts of ammonia and 109 parts of water were evolved. The solidobtained weighed 38.6 parts and was high grade sodium fluoride. Itcontained no ammonia.

Example H 31.38 parts of KRZH O, 37.04 parts of NHQE and 11.61 parts B 0were placed in 100 parts of water. The solution was evaporated todryness. 17.0 parts of ammonia and 121 parts of water were evolved. 43parts of solid were obtained which was practically pure potassiumfluoborate. The solid contained no ammonia.

Example III 20.67 parts or" NaHF 19 parts of NH HF and 11.61 parts of B0 were placed in 100 parts of water. The solution was evaporated todryness to remove 5.67 parts of ammonia and 109 parts of water. Thesolid was practically pure sodium fluoborate.

Example IV 26.04 parts of Kl-lF 19 parts of NH HF and 11.61 parts of B 0were placed in 100 parts of water. The solution was evaporated todryness to remove 5.67 parts of ammonia and 109 parts of water. Thesolid was practically pure potassium fluoborate. The solid containedpractically no ammonia.

In the foregoing description, I have described such details of procedureas are necessary to enable one skilled in the art of which thisinvention relates to practice the invention. Procedures such as theacidification and subsequent treatment of phosphate rock, the scrubbingof fluorine-containing gases with water, and the manner in whichsolutions to be reacted are mixed and precipitates are filtered andwashed are carried out by means well known to those skilled in the art.

I claim:

1. A process for the production of alkali metal fluoborates consistingof chemicaliy combining alkali metal fluoride with stoic'niometricquantities of a single reactant from each of the two groups consistingof ammonium fluoride and ammonium acid fluoride, and boric acid andboric oxide in aqueous solution, evaporating said solution to drynessthereby driving off water and ammonia, and recovering solid alkali metalfluoborate.

2. In a process for the production of alkali metal fluoborates fromalkali metal fluoride along with stoichiometric quantities of a memberfrom the group consisting of ammonium acid fluoride and ammoniumfluoride and a member from the group consisting of boric acid and boricoxide the steps of: forming an aqueous solution of the aforementionedreactants, heating said solution to drive off all ammonia and Water,thereby forming a solid mass consisting of alkali metal fluoborate andpurifying said alkali metal fiuoborate by crystallization from Water.

3. In a process for the production of pure alkali metal fiuoborates fromalkali metal fluoride along with a mem her from the group consisting ofammonium acid fluoride and ammonium fluoride and a member from the groupconsisting of boric acid and boric oxide the steps of: forming anaqueous solution of the aforementioned reactants in stoichiornetricratio, raising the temperature to the point where all ammonia and waterare driven off resulting in a solid mass, said mass consisting ofsubstantially pure alkali metal fluoborate and further purifying saidalkali metal fiuoborate by crystallization from Water.

4. In a process or the production of alkali metal fiuoborate from alkalimetal fluoride along with stoichiometric quantities of a member from thegroup consisting of ammonium acid fluoride and ammonium fluoride, and amember from the group consisting of boric acid and boric oxide the stepsof: combining the aforementioned reactants as solids in a limited amountof water so that a slurry is produced, and heating said slurry to driveoff all ammonia and water, thereby forming a solid mass consisting ofalkali metal fiuoborate, and purifying said alkali metal fluoborate bycrystallization from water.

5. In a process for the production of pure alkali metal fluoborates fromalkali metal fluoride along with a memher from the group consisting ofammonium acid fluoride and ammonium fluoride and a member from the groupconsisting of boric acid and boric oxide the steps of: combining theaforementioned reactants in stoichiomctric ratio as solids in a limitedamount of water such that a slurry is produced, raising the temperatureto the point Where all ammonia and water are driven ofi resulting in asolid mass, said mass consisting of substantially pure alkali metalfluoborate and further purifying said alkali metal fluo'ocrate bycrystallization from water.

References Cited in the file of this patent Mellor: ComprehensiveTreatise on Inorganic and Theoretical Chemistry, Longmans Green & (30.,New York, 1923, vol. 5, pages 126 and 127.

1. A PROCESS FOR THE PRODUCTION OF ALKALI METAL FLUOBORATES CONSISTINGOF CHEMICALLY COMBINING ALKALI METAL FLUORIDE WITH STOIC HIOMETRICQUANTITIES OF A SINGLE REACTANT FROM EACH OF THE TWO GROUPS CONSISTINGOF AMMONIUM FLUORIDE AND AMMONIUM ACID FLUORIDE, AND BORIC ACID ANDBORIC OXIDE IN AQUEOUS SOLUTION, EVAPORATING SAID SOLUTION TO DRYNESSTHEREBY DRIVING OFF WATER AND AMMONIA, AND RECOVERING SOLID ALKALI METALFLUOBORATE.